Accurate and reliable transmission of analog electronic data from a source of measurement to a circuit for analysis is required in many applications. If excessive noise is present on the transmission line, analog data is subject to misinterpretation. Further, if the signal becomes too weak or the connection poor, or if components in sensitive analog sensing circuits drift over time, data is lost or is misrepresented. Many of the previous techniques for transmitting analog data over transmission lines were subject to these and other problems.
Two wires are usually required to provide power to an electrically operated sensor used in an existing system. Adding the capability to transmit analog data over existing systems having only two wires is often required. In the past, adapting a two-wire power system to accurately and reliably carry analog data has been difficult. Because a power line is susceptible to noise caused by stray electromagnetic fields, changes in power draw, spikes, and the like, accurate transmission of data over the power line is difficult. The problems of noise in the circuit and on a power line are compounded when sending analog data due to component aging or temperature drifts in sensitive analog sensing circuits, which create false data readings that are difficult or impossible to discover.
Transmitting analog data from multiple sensors to each other or to a central processor over the two-wire power line creates additional significant difficulties. Individual sensors must be identified, both for sending and receiving purposes. The complexity of the system is therefore significantly increased if multiple sensors must transmit data on the same two-wire power line.